NSFetchedResultsController fetch request - updating predicate and UITableView

In my iPhone Core Data app I have it configured in a master-detail view setup.

The master view is a UITableView that lists objects of the List entity. The List entity has a to-many relationship with the Task entity (called "tasks"), and the Task entity has an inverse to-one relationship with List called "list".

When a List object is selected in the master view, I want the detail view (another UITableView) to list the Task objects that correspond to that List object. What I've done so far is this:

In the detail view controller I've declared a property for a List object:

@property (nonatomic, retain) List *list;

Then in the master view controller I use this table view delegate method to set the list property of the detail view controller when a list is selected:

- (void)tableView:(UITableView *)aTableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSManagedObject *selectedObject = [[self fetchedResultsController] objectAtIndexPath:indexPath];
    detailViewController.list = (List*)selectedObject; 
}

Then, I've overriden the setter for the list property in the detail view controller like this:

- (void)setList:(List*)newList
{
    if (list != newList) {
        [list release];
        list = [newList retain];

        NSPredicate *newPredicate = [NSPredicate predicateWithFormat:@"(list == %@)", list];
        [NSFetchedResultsController deleteCacheWithName:@"Root"];
        [[[self fetchedResultsController] fetchRequest] setPredicate:newPredicate];

        NSError *error = nil;
        if (![[self fetchedResultsController] performFetch:&error]) {
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }       
    }
}

What I'm doing here is setting a predicate on the fetched results to filter out the objects so that I only get the ones that belong to the selected List object. The fetchedResultsController getter for the detail view controller looks like this:

- (NSFetchedResultsController *)fetchedResultsController {
    if (fetchedResultsController == nil) {
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Task" inManagedObjectContext:managedObjectContext];
        [fetchRequest setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"FALSEPREDICATE"];
    [fetchRequest setPredicate:predicate];

        NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
        NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

        [fetchRequest setSortDescriptors:sortDescriptors];

        NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
        aFetchedResultsController.delegate = self;
        self.fetchedResultsController = aFetchedResultsController;

        [aFetchedResultsController release];
        [fetchRequest release];
        [sortDescriptor release];
        [sortDescriptors release];
    }

    return fetchedResultsController;
}

Its almost unchanged from the default in the Core Data project template, the change I made is to add a predicate that always returns false, the reason being that when there is no List selected I don't want any items to be displayed in the detail view (if a list is selected the predicate is changed in the setter for the list property).

However, when I select a list item, nothing really happens. Nothing in the table view changes, it stays empty. I'm sure my logic is flawed in several places, advice is appreciated

Thanks

You don't need to set up a NSFetchedResultsController for your task list. Since you are passing in the List entity, you can just ask the List entity for the tasks:

NSSet *tasks = [[self list] valueForKey:@"tasks"];
NSSortDescriptor *sort = ...;
NSArray *sorted = [[tasks allObjects] sortedArrayUsingDescriptors:[NSArray arrayWithObject:sort]];
[self setTasks:sorted];

Then have the UITableviewDatasource methods run off of that tasks array.

Maybe I don't understand your setup completely, but